Re: [PATCH net] ptr_ring: prevent integer overflow when calculating size

[Michael S. Tsirkin]

On Sun, Feb 11, 2018 at 11:28:12AM +0800, Jason Wang wrote:
> Switch to use dividing to prevent integer overflow when size is too
> big to calculate allocation size properly.
> 
> Reported-by: Eric Biggers <ebiggers3@xxxxxxxxx>
> Fixes: 6e6e41c31122 ("ptr_ring: fail early if queue occupies more than KMALLOC_MAX_SIZE")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>

Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

> ---
>  include/linux/ptr_ring.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index b884b77..e633522 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -469,7 +469,7 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
>   */
>  static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
>  {
> -	if (size * sizeof(void *) > KMALLOC_MAX_SIZE)
> +	if (size > KMALLOC_MAX_SIZE / sizeof(void *))
>  		return NULL;
>  	return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO);
>  }
> -- 
> 2.7.4